Production method for civil mixed fuel gas consisting of light hydrocarbons mixed with air and coal

ABSTRACT

A production method for civil mixed fuel gas with light hydrocarbons mixed with air and coal gas, which is characterized in that the preparation method of the said civil mixed fuel gas is as follows: a. filtering liquid light hydrocarbons, and pressuring; b. heating and gasifying the light hydrocarbons in the heating gasifier; c. mixing gasified hydrocarbons with air or pressured air in a mixing chamber to form a mixture of light hydrocarbons and air; d. storing the mixture in a middle gas-storing tank after measured by oxygen meter; e. mixing coal gas and light hydrocarbons mixed with air in a gas-mixing chamber to form mixed fuel gas; f. storing the mixed fuel gas in a gas-storing tank after measured by oxygen meter; g. transmitting and distributing the mixed fuel gas to user terminal in a low or middle and low pressure two grade form. The present invention makes use of the liquid hydrocarbons with boiling range below 80 deg. C. which is mixed with air in proportional after gasified, and the mixture is further mixed with various coal gas in proportional. This invention can increase the heat value of the fuel gas and enlarge the capacity, and reduce the volume content of carbon monoxide. The mixed fuel gas reaches the national combustion need of manual coal gas.

FIELD OF THE INVENTION

The invention involves in technical field of civil fuel gas, i.e., forming civil pipeline fuel gas by mixing light hydrocarbons with kinds of coal gas and its preparation method.

BACKGROUND OF THE INVENTION

In recent years, as price of hydrocarbon fuel gas is increasing and developed countries lay great emphasis on environment protection, clean fuel with slight harmful gas emission is highly required. Premier of the State Council Wen Jiabao presided over standing conference of the State Council on Jun. 30, 2004, discussed and in principle passed the Outline of Medium and Long Term Development Plan for Energy (2004-2020), focus of which is to step on energy development road of Chinese Characteristics. On Lecture held on by the State Council on Aug. 24, 2004, Premier Wen reemphasized on to put saving and using oil and gas resource effectively at the first place to ensure long term supply and effective utility of oil gas resource.

National economic development promotes development of civil infrastructure construction. Civil fuel gas industry is developing into a leading and influential basic industry for national economy, which is also one of important industry under fostering of the central government. At present, there're about 500 large and medium cities where fuel gas facilities are installed, and there're still over 1000 cities where history of pipeline fuel gas is empty. In some cities, civil pipeline fuel gas industry step on its way of development in 1970s and 1980s. In some other cities, semi-water gas, water gas or industry off-gas are used as main gas source, which is featured of low heat value and excessive carbon monoxide. As a result, the gas is of severe toxicity and human's life is threatened once there's any gas leakage. The gas will be replaced by other gas if no improvement is made to such gas of low heat value of high content of carbon monoxide due to its small heat value, less than 3000 kcal/nm³, which is far away from standard of civil pipeline fuel gas of 3500 kcal/nm³, co≦20% (volume).

With development of urban economy and urbanization of rural areas, city proper is expanding and citizens are increasingly growing. There're about 15 to 20 million population changing from rural to non-rural. As a result, pressure for each city is increasing, especially the production and supply of fuel gas, which is far beyond needs of citizen's daily life.

However, it is impossible to improve heat value and enlarge the capacity of semi-water gas, water gas and industry off-gas based on original manufacturing facilities. If we want to enlarge the capacity of original qualified manual coal gas, we need to invest huge money to increase equipments in traditional method. However, most construction and operation unit can't afford so much investment. For general coal gas, cost of each 1000 kcal coal gas is about RMB 0.35-0.5 from perspective of heat value. Each household will consume about 6500 kcal on average, therefore, cost per day for each household is RMB 2.28-3.25 and cost per month for household is RMB 68.4-97.5. In the past, civil coal gas industry is a kind of welfare of government. Therefore, the government spent lots of governmental expenses for coal gas industry, i.e., the more gas is produced, gas consumption is larger and governmental subsidy is greater than before. However, Enterprise develops not as good as expected, and then policy of limited coal gas consumption and negotiated price for over limit consumption is carried out in most cities (ever carried out in Shanghai). Once the government stops providing subsidy, those enterprises are hard to survive, let alone further development.

Petrol consumption of China in 2003 accounted for 7.4% of world petrol consumption. In that year, China's byproduct of oil refining, light hydrocarbons, reached 4.64 million ton, while world oil refining byproduct reached 62.70 million ton. If all those byproducts are used for manufacturing fuel gas, 330 million pipeline fuel gas users will benefit from it. Assuming there're 3.2 people in each household, about 1 billion people will benefit from it. The above figure doesn't contain byproduct of petrochemical ethylene engineering, light hydrocarbon and condensed light hydrocarbons of natural gas. Therefore, light hydrocarbon mixed with air and coal gas, not only increases heat value, but also enlarges the capacity, and could be supplementary, peak-shaving and standby civil fuel gas replacing natural gas. It is prospective to solve the difficulty of expansion for cities where coal gas supply lagged behind population development.

-   1. Mixed fuel gas of manual coal gas standard produced by mixing     light hydrocarbons and coal gas for purpose of making full use of     original gas production and supply system could be used as civil     pipeline gas as it satisfies manual coal gas in combustion     characteristics and complies with normal combustion of manual coal     gas appliance in fixed shape. -   2. Semi-water gas, water gas and industry off-gas after mixed with     light hydrocarbons meet National Civil Fuel Gas Standard. The gas     appliance thus used could also be manufactured and sold as per     applicable standard. -   3. Once natural or liquefied natural gas are supplied in the city,     light hydrocarbon mixed with air could be replaced gas and peak     shaving gas as well as standby gas source.

Light hydrocarbon mixed with air is advantageous in following aspects:

-   1. Main raw material of the mixed fuel gas is light hydrocarbon,     which is from byproducts of oil refining plant, petrochemical     engineering plant and natural gas condensation, and is characterized     of huge source, low price and high heat value. -   2. Light hydrocarbon with air, as additive of increasing heat value     and enlarge the capacity, makes the mixed fuel gas meet national     fuel gas standard after it is mixed with such unacceptable     semi-water gas, water gas and industry off-gas. Light hydrocarbon     mixed with air and coal gas not only increases heat value and     enlarge the capacity, but also reduce content of carbon monoxide:     heat value of mixed fuel gas is 1.4-1.9 times of original coal gas,     and the capacity is 1.0-1.5 times of original gas, which indicates     that combustion characteristics of the mixed fuel gas meets national     standard and the mixed fuel gas is suitable for gas appliance in     fixes shape. -   3. Light hydrocarbon mixed with air could be used as peak-shaving     gas and standby gas. The preparation speed is quite fast and only     several quarters are needed from production to full load. However,     it takes several days for coal gas. Therefore, light hydrocarbon     mixed with air is more suitable to be used as emergency gas. -   4. Hydrocarbon mixed with air is a kind of safe gas with low     toxicity and explosion possibility. In addition, dewpoint     temperature of the mixed fuel gas is quite low and it adaptable for     various environments. -   5. Gas production process for light hydrocarbon fuel gas is quite     simple and equipment cost is also lower than that of liquefied     petroleum gas. Cost of gas production is about 25%-40% lower than     that of original coal gas per heat value unit. However, heat value     is quite high and the mixed fuel gas is reliable and safe, suitable     for pipeline delivery.

There's usually only single gas source when a city or region begins to use gas fuel. With the growing of civil gas demand and demand of heat value adjustment and peak shaving, several other gas production processes come up to meet social demands, for example, gas production not via normal procedure and gas production via mixing light hydrocarbon with air and coal gas. Although there're multiple gases and different preparation proportion for different gas in the mixed fuel gas, combustion characteristics is still the same as before and the mixed fuel gas is still suitable for previous gas appliance.

Since China is a country of vast lands and huge population, coexisting of several gas sources will last for some time even though more natural gas are discovered and explored.

According to related source, petroleum consumption for 2003 is 270 million tons, and natural gas consumption is over 30 billion m³. It is estimated that petroleum demand will increase to 400 million tons by 2020. From structure of natural gas consumption, consumption of natural gas for electricity generation and civil fuel gas increases faster than other applications. Natural gas consumption proportion in primary energy consumption will increase from current 3% to 10%. In addition, on basis of 1.72% oil refining amount, light hydrocarbon, as oil refining byproduct, reached 4.64 million tons in 2003. Price of light hydrocarbon is quite low, about 70-80% of liquefied petroleum gas, while heat value per kg is 10%-15% higher than that of liquefied petroleum gas. Therefore, light hydrocarbon mixed with air and various coal gases will increase heat value and enlarge the capacity, which is economic and ideal as follows: the mixed fuel gas is of low toxicity and high heat value and increases to 1.0-2.5 times of civil fuel gas. Therefore, it is a subject matter under discussion to convert light hydrocarbon mixed with air to civil fuel gas in recent years.

SUMMARY OF THE INVENTION

The invention intends to provide an improved preparation method for civil mixed fuel gas with light hydrocarbons mixed with air and coal gas so as to avoid such shortage of existing coal gas as high cost, limit heat value, server toxicity.

For purpose to achieve above mentioned objectives, technical scheme of the invention is as follows: A production method for civil mixed fuel gas with light hydrocarbons mixed with air and coal gas, which is characterized in that the preparation method of the said civil mixed fuel gas is as follows: a. filtering liquid light hydrocarbons, and pressuring; b. heating and gasifying the light hydrocarbons in the heating gasifier; c. mixing gasified hydrocarbons with air or pressured air in a mixing chamber to form a mixture of light hydrocarbons and air; d. storing the mixture in a middle gas-storing tank after measured by oxygen meter; e. mixing coal gas and light hydrocarbons mixed with air in a gas-mixing chamber to form mixed fuel gas; f. storing the mixed fuel gas in a gas-storing tank after measured by oxygen meter; g. transmitting and distributing the mixed fuel gas to user terminal in a low or middle and low pressure two grade form.

The present invention makes use of the liquid hydrocarbons with boiling range below 80 deg. C. which is mixed with air in proportional after gasified, and the mixture is further mixed with various coal gas in propotional, this invention can increase the heat value of the fuel gas and enlarge the capacity, and reduce the volume content of carbon monoxide, the mixed fuel gas reaches the national combustion characteristics need of manual coal gas.

The said mixed fuel gas is advantageous in following aspects:

-   1. Turning gas production enterprise from deficit into profit. If     there's no more burden to users and government's subsidy is     decreasing year by year, enterprise will benefit from the invention     of mixed fuel gas. -   2. Volume content of CO for civil manual coal gas must be less than     20% according to national provisions. However CO content is 34.4%     for water gas and 30.9% for carbureted coal gas. CO content of     manual coal gas in some cities is sometimes over limit. As CO is of     sever toxicity and it is common to hear intoxication accident due to     coal gas leakage. However, CO content of improved civil fuel gas is     less than 20%, which indicates lower toxicity. -   3. Original city transmitting and distribution pipeline could also     be used to enlarge the capacity, which will save a lot of investment     in distribution pipeline with large diameter. As differential     pressure per unit length of improved mixed fuel gas is about 75% of     that in original civil fuel gas, gas supply amount could be     increased appropriately in original pipeline. -   4. Compared with original civil fuel gas, heat value of the said     mixed fuel gas is 40% higher and output also increases by 67%, and     total amount increases by 130%. If there're 100,000 users for     original civil fuel gas, improved mixed fuel gas can meet gas supply     demand of 230,000 users. -   5. Relative specific weight of mixed fuel gas is smaller than that     of air. Therefore, the gas is easy to diffuse instead of coagulate     once there's any leakage. Possibility of explosion is quite slim and     it is safer to use. -   6. Natural gas could be mixed with improved fuel gas in proper     proportion for civil fuel gas. As the combustion characteristics is     the same, several gas source could be replaced one another, which is     in need of civil fuel gas supply. With improvement of combustion     conditions, environment condition and kitchen environment should be     improved accordingly.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is process flowchart of the invention

FIG. 2 is another process flowchart of the invention.

DETAILED DESCRIPTION OF EMBODIMENTS OF THE INVENTION

Below is further description of the invention based on figures and embodiments.

A production method for civil mixed fuel gas with light hydrocarbons mixed with air and coal gas, which is characterized in that the preparation method of the said civil mixed fuel gas is as follows: a. filtering liquid light hydrocarbons, and pressuring; b. heating and gasifying the light hydrocarbons in the heating gasifier; c. mixing gasified hydrocarbons with air or pressured air in a mixing chamber to form a mixture of light hydrocarbons and air; d. storing the mixture in a middle gas-storing tank after measured by oxygen meter; e. mixing coal gas and light hydrocarbons mixed with air in a gas-mixing chamber to form mixed fuel gas; f. storing the mixed fuel gas in a gas-storing tank after measured by oxygen meter; g. transmitting and distributing the mixed fuel gas to user terminal in a low or middle and low pressure two grade form, wherein the mixed fuel gas is composed of 1.6-10% light hydrocarbon fuel gas, 4-36% air and 55-94.4% coal gas.

A production method of civil mixed fuel gas with light hydrocarbons mixed with air and coal gas, which is characterized in that the preparation method of the said civil mixed fuel gas is as follows: a. filtering liquid light hydrocarbons with a 200-mesh strainer and pressuring liquid light hydrocarbons mixed air which is subject to drain spray mixing to ≧3 kg/cm² and liquid light hydrocarbons mixed air which is subject to isopiestic mixing to ≧0.8 kg/cm² respectively; b. heating and gasifying light hydrocarbons in the heating gasifier to a temperature ≧110° C. for light hydrocarbons subject to drain spray mixing and to a temperature ≧80° C. for light hydrocarbons subject to isopiestic mixing respectively; c. mixing gasified hydrocarbons with air or pressured air in a mixing chamber to form a mixture of light hydrocarbons and air; d. storing the mixture in a middle gas-storing tank after measured by oxygen meter; e. storing the mixture of natural gas, coal gas and light hydrocarbons mixed with air after oxygen content is measured acceptable by oxygen meter; f. transmitting and distributing the said mixed fuel gas to user terminal in a low or middle and low pressure two grade form, wherein mixed fuel gas is composed of 4.8-34% natural gas, 8-31.8% air, 1.6-8% light hydrocarbon fuel gas and 50-70.6% coal gas.

Oxygen content measured by oxygen meter in above process should reach 0.5-10%. Liquid light hydrocarbon is a compound of over following one or two substances: by-product liquid light hydrocarbon in petrochemical engineering, decomposed light hydrocarbon in petrochemical engineering or condensate light hydrocarbon in petrol and natural gas.

The transmitting and distribution pressure is integrated with urban pipeline pressure grade. Low pressure in pipeline distribution refers to pressure smaller than or equal to 500 mmH₂O-0.1 Mpa. In the process of carrying out the invention, volume content of combustible gas in the mixed fuel gas is great than 1.7 times of upper limit to gas explosion. Therefore, the mixed fuel gas is far beyond danger of explosion. Dewpoint temperature of mixed fuel gas is −8° C. under 0.1 Mpa distribution pressure. As city distribution pipeline are buried beneath frozen ground layer, civil mixed fuel gas of the invention is strongly adaptable to different region conditions.

Light hydrocarbon mixed with air, additive of increasing heat value and capacity, is produced at low cost of RMB 0.24/1000 Kcal, 48-70% of original coal gas. Therefore monthly expense for users of mixed light hydrocarbon fuel gas is greatly decreased as the gas production cost is decreasing and output is increasing. As a result, number of users will increase and operation cost for enterprise will decrease. The mixed fuel gas will bring benefits and safeness in various aspects due to low cost and multiple gas sources.

Embodiment 1

In a certain city, it was assumed 100,000 household used manual pipeline coal gas at 5 R Standard. With expansion of the city proper and increasing of population, original manual coal gas couldn't meet demands of new increased coal gas users. The original gas supply was only enough to maintain supply for old users. It was estimated that coal gas user would increase to 200,000 in following 5 years. Therefore, light hydrocarbon mixed with air and coal gas was the best choice to increase heat value and enlarge gas supply capacity, which meant gas supply of 200,000 households in following five years could be satisfied and amount of gas supplied could be increased gradually based on pipeline expansion. Preparation methods were as follows: filtering liquid light hydrocarbon with a 200-mesh strainer and then pressing to pressure of 1.2 kg/cm²; heating and gasifying liquid light hydrocarbon in a heating gasifier to make it under pressure of or over 0.6 kg/cm²; mixing light hydrocarbon with air in proportion of 1:4 in mixing chamber, i.e., 1 unit light hydrocarbon and 4 units air measured with meter, where O₂ content was 17.2%; storing the mixed fuel gas in a gas-storing tank after it was measured acceptable with oxygen meter; following steps below for mixing proportion at different stages in terms of increased users:

When users increased to 115,000 households (15000 users increased), 92% manual coal gas and 8% light hydrocarbon mixed with air (where light hydrocarbon accounts for 1.6% and air accounts for 6.4%) were mixed and then heat value increased from 3780 Kcal/nm³ to 4084 Kcal/nm³, output increased by 8.7% and total amount increased to 117.4%;

When users increased to 125,000 households, 88% manual coal gas and 12% light hydrocarbon mixed with air (where light hydrocarbon accounts for 2.4% and air accounts for 9.6%) were mixed and then heat value increased to 4235 Kcal/nm³, output increased by 13.6% and total amount increased to 127.3%;

When users increased to 135,000 households, 84% manual coal gas and 16% light hydrocarbon mixed with air (where light hydrocarbon accounts for 3.2% and air accounts for 12.8%) were mixed and then heat value increased to 4388 Kcal/nm³, output increased by 19% and total amount increased to 138.5%;

When users increased to 150,000 households, 80% manual coal gas and 20% light hydrocarbon mixed with air (where light hydrocarbon accounts for 48% and air accounts for 16%) were mixed and then heat value increased to 4540 Kcal/nm³, output increased by 25% and total amount increased to 150.11%;

When users increased to 160,000 households, 76% manual coal gas and 24% light hydrocarbon mixed with air (where light hydrocarbon accounts for 4.8% and air accounts for 19.2%) were mixed and then heat value increased to 4692 Kcal/nm³, output increased by 31.6% and total amount increased to 163.33%;

When users increased to 175,000 households, manual coal gas were mixed with 28% light hydrocarbon mixed with air (where light hydrocarbon accounts for 5.6% and air accounts for 22.4%) and then heat value increased to 4844 Kcal/nm³, output increased by 38.9% and total amount increased to 177.93%;

When users increased to 190,000 households, 68% manual coal gas and 32% light hydrocarbon mixed with air (where light hydrocarbon accounts for 6.4% and air accounts for 25.6%) were mixed and then heat value increased to 4995 Kcal/nm³, output increased by 47% and total amount increased to 194.25%;

When users increased to 200,000 households, 64% manual coal gas and 36% light hydrocarbon mixed with air (where light hydrocarbon accounts for 7.2% and air accounts for 28.8%) were mixed and then heat value increased to 5147 Kcal/nm³, output increased by 56.3% and total amount increased to 212.5%;

When gas consumption demand was increasing for reasons of seasonal difference, improvement of user's living standard and holidays and festival, 60% manual coal gas and 40% light hydrocarbon mixed with air (where light hydrocarbon accounts for 8% and air accounts for 32%) were mixed and then heat value increased to 5300 Kcal/nm³, output increased by 67% and total amount increased to 233.63%. In this case, there was 16.8% maximum remaining gas which could be used for standby and peak shaving purpose or for fuel gas air conditioning to release urban power supply pressure.

For all above mixed fuel gas with different mixing proportion, combustion characteristics comply with 5 R Standard of original coal gas, CO content decreases substantially from 17.9% to 10.74%, content of combustible gas and upper limit of explosion are from 1.87 times to 1.95 times of those of original manual coal gas respectively.

As the whole process from preparation to full-load production only takes several quarters, it is quite flexible for production scheduling. In addition, light hydrocarbon is an oil refining byproduct and in low price. Therefore unit heat value price of the mixed fuel gas is decreasing and production cost is decreasing accordingly, which benefits to users and turns gas production enterprise from deficit to profit. Light hydrocarbon mixed with air and coal gas is flexible, variable, economical, safe and practical to maximum extent.

Property parameters of mixed fuel gas which is prepared by mixing the invented fuel gas and 5 R civil coal gas is shown in Table 1. Property parameters of mixed fuel gas which is prepared by mixing the invented fuel gas and 6 R civil coal gas is shown in Table 2. Property parameters of mixed fuel gas which is prepared by mixing the invented fuel gas and 7 R civil coal gas is shown in Table 3.

TABLE 1 200,000 household: main pipe diameter 0.8 m transmitting Light Wobbe Com- pressure 0.1 Mpa Total hydro- Heat value index W bustion Combustible gas unit pressure and amount Carbureted Natural carbon Air MJ/Nm³ MJ/m³ potency CO concentration max. transmitting increased S/N water gas % gas % % % (Kcal/Nm³) (Kcal/m3) CP O₂ % % %/UEL distance to 1 70 6 24    18.72    21.1 64.09 5.15 13.65 64 ÷ 39.65 = 9500 ÷ 0.895 = 203 (4472) (5041) 1.61 10.61 Km 2 65 7 28    19.65    21.69 61.93 5.98 12.68 61.4 ÷ 9500 ÷ 0.848 = 230 (4694) (5180) 36.89 = 11.2 Km 1.66 3 60 8 32    20.58    22.25 59.95 6.82 11.7 56 ÷ 34.22 = 9500 ÷ 261 (4915) (5314) 1.64 4 55 9 36    21.51    22.8 58.08 7.65 10.73 53 ÷ 30.7 = 9500 ÷ 0.767 = 297 (5137) (5446) 1.73 12.38 Km 5 55 6 7.2 31.8    21.08    23.0 57.35 6.68 10.73 57.14 ÷ 9500 ÷ 0.758 = 292 (5035) (5492) 30.92 = 12.53 Km 1.85 6 55 9 6.3 29.7    20.87    23.11 57.26 6.24 10.73 59.21 ÷ 9500 ÷ 0.749 = 289 (4984) (5519) 30.6 = 12.68 Km 1.94 7 55 12 5.4 27.6    20.65    23.22 57.25 5.8 10.73 61.28 ÷ 9500 ÷ 0.74 = 286 (4933) (5546) 30.3 = 12.84 Km 2.02 8 55 15 4.5 25.5    20.44    23.35 57.34 5.36 10.73 63.35 ÷ 9500 ÷ 0.731 = 283 (4882) (5578) 29.82 = 13 Km 2.14 9 55 18 3.6 23.4    20.23    23.5 57.51 4.91 10.73 65.42 ÷ 9500 ÷ 0.72 = 280 (4831) (5613) 29.72 = 13.19 Km 2.2 10 55 21 2.7 21.3    20.01    23.64 57.81 4.47 10.73 67.49 ÷ 9500 ÷ 0.706 = 277 (4780) (5647) 29.6 = 13.46 Km 2.28 11 55 24 1.8 19.2    19.80    23.82 58.25 4.03 10.73 69.56 ÷ 9500 ÷ 0.69 = 274 (4729) (5688) 29.33 = 13.77 Km 2.37 12 55 30 15    19.37    24.19 59.51 3.15 10.73 73.7 ÷ 9500 ÷ 0.681 = 268 (4627) (5777) 28.34 = 13.94 Km 2.6

TABLE 2 200,000 Comparison household: main between UEL × pipe diameter 1.5 0.8 m transmitting Pressure Wobbe and pressure 0.1 Mpa gasified (humid) Light Heat value index W Combustion Combustible unit pressure and coal Natural hydrocarbon Air MJ/Nm³ MJ/m³ potency gas max. transmitting S/N gas % gas % % % (Kcal/Nm³) (Kcal/m3) CP O₂ % CO % concentration % distance 1 100 17.08 (4079) 26.47 (6322) 114 0.3 18 40.5 × 1.5 = 60.8 < 9500 ÷ 92.7 0.558 = 17.03 Km 2 93.6 1.6 4.8 18.52 (4424) 27.08 (6468) 102 1.29 16.9 38.1 × 1.5 = 57.2 < 9500 ÷ 88.4 0.544 = 17.46 Km 3 90.4 2.4 7.2 19.24 (4596) 27.28 (6515) 97 1.78 16.3 36.8 × 1.5 = 55.2 < 9500 ÷ 86.2 0.536 = 17.72 Km 4 87.2 3.2 9.6 19.97 (4770) 27.51 (6570) 92 2.28 15.7 35.6 × 1.5 = 53.4 < 9500 ÷ 84 0.527 = 18.03 Km 5 84 4 12 20.69 (4942) 27.73 (6622) 88 2.77 15.1 34.5 × 1.5 = 51.8 < 9500 ÷ 81.9 0.519 = 18.3 Km 6 80.8 4.8 14.4 21.42 (5115) 27.97 (6680) 85 3.27 14.5 33.3 × 1.5 = 50 < 9500 ÷ 79.7 0.51 = 18.63 Km 7 77.6 5.6 16.8 22.14 (5287) 28.21 (6737) 81 3.76 14 32.4 × 1.5 = 48.6 < 9500 ÷ 76.6 0.502 = 18.92 Km 8 74.4 6.4 19.2 22.86 (5460) 27.82 (6644) 79 4.26 13.4 31 × 1.5 = 46.5 < 9500 ÷ 75.4 0.515 = 18.45 Km 9 68 8 24 24.31 (5805) 28.95 (6915) 73.4 5.25 12.2 28.8 × 1.5 = 43.2 < 9500 ÷ 71 0.476 = 19.96 Km 10 60 8 32 22.94 (5478) 26.44 (6315) 70.1 6.9 10.8 27.8 × 1.5 = 41.7 < 9500 ÷ 63.6 0.571 = 16.64 Km 11 55 30 15 20.42 (4877) 27.27 (6513) 69.7 3.32 9.9 25.3 × 1.5 = 38 < 9500 ÷ 79.9 0.537 = 17.69 Km 12 55 24 1.8 19.2 21.07 (5032) 27.03 (6455) 68.1 4.2 9.9 25.5 × 1.5 = 38.3 < 9500 ÷ 75.9 0.546 = 17.4 Km 13 55 15 4.5 25.5 22.05 (5265) 26.77 (6394) 66.9 5.52 9.9 25.7 × 1.5 = 38.6 < 9500 ÷ 69.9 0.557 = 17.06 Km 14 55 6 7.2 31.8 23.02 (5499)  26.6 (6354) 66.8 6.84 9.9 26 × 1.5 = 39 < 64 9500 ÷ 0.563 = 16.87 Km 15 55 9 36 23.67 (5654) 26.54 (6338) 67.2 7.73 9.9 26.2 × 1.5 = 39.3 < 9500 ÷ 60 0.568 = 16.73 Km

TABLE 3 Comparison between UEL × 200,000 household: 1.5 main pipe diameter Wobbe and 08 m transmitting Coke (Dry) Light Heat value index W Combustion Combustible pressure 0.1 Mpa unit coal Natural hydrocarbon Air MJ/Nm³ MJ/m³ potency CO gas pressure and max. S/N gas % gas % % % (Kcal/Nm³) (Kcal/m3) CP O₂ % % concentration % transmitting distance 1 100    19.82 32.92 (7865) 121 1.2 8.6 34.5 × 1.5 = 51.7 < 9500 ÷ 0.368 = 25.83 Km (4734) 93.2 2 94.4 1.6 4    21.25  32.8 (7835) 109.5 1.97 8.1 33.4 × 1.5 = 50.1 < 9500 ÷ 0.371 = 25.63 Km (5075) 89.6 3 91.6 2.4 6    21.96  32.8 (7834) 104.5 2.36 7.9 32.4 × 1.5 = 48.6 < 9500 ÷ 0.371 = 25.63 Km (5245) 87.8 4 88.8 3.2 8    22.68 32.85 (7846) 100.1 2.75 7.6 31.3 × 1.5 = 47 < 9500 ÷ 0.37 = 25.68 Km (5417) 86 5 86 4 10    23.39  32.9 (7858) 96 3.13 7.4 30.2 × 1.5 = 45.3 < 9500 ÷ 0.368 = 25.82 Km (5587) 84.2 6 83.2 4.8 12    24.11   33 (7881) 92.4 3.52 7.2 29.2 × 1.5 = 43.8 < 9500 ÷ 0.366 = 25.96 (5758) 82.34 7 80.4 5.6 14    24.82  33.1 (7903) 89.1 3.9 6.9 28.2 × 1.5 = 42.3 < 9500 ÷ 0.364 = 26.1 Km (5928) 80.53 8 77.6 6.4 16    25.54 33.22 (7933) 86 4.29 6.7 27.2 × 1.5 = 40.8 < 9500 ÷ 0.362 = 26.24 Km (6099) 78.72 9 72 8 20    26.96 33.48 (7996) 80.7 5.06 6.2 26.2 × 1.5 = 39.3 < 9500 ÷ 0.356 = 26.69 Km (6439) 75.1 10 70.6 5 6.4 18    26.17 33.38 (7972) 80.5 4.63 6.1 26 × 1.5 = 39 < 9500 ÷ 0.358 = 26.54 Km (6250) 77.15 11 69.9 7.5 5.6 17    25.77 33.34 (7962) 80.5 4.41 6 25.9 × 1.5 = 38.9 < 9500 ÷ 0.359 = 26.46 Km (6156) 78.2 12 69.2 10 4.8 16    25.38 33.31 (7955) 80.6 4.19 6 25.8 × 1.5 = 38.7 < 9500 ÷ 0.36 = 26.39 Km (6062) 79.2 13 68.5 12.5 4 15    24.98 33.27 (7945) 80.7 3.97 5.9 25.7 × 1.5 = 38.6 < 9500 ÷ 0.36 = 26.39 Km (5967) 80.2 14 67.8 15 3.2 14    24.59 33.25 (7942) 81 3.75 5.8 25.7 × 1.5 = 38.6 < 9500 ÷ 0.361 = 26.32 Km (5873) 81.2 15 67.1 17.5 2.4 13    24.19 33.23 (7936) 81.2 3.54 5.8 25.6 × 1.5 = 38.4 < 9500 ÷ 0.361 = 26.32 Km (5777) 82.3 16 66.4 20 1.6 12    23.79 33.21 (7932) 81.6 3.32 5.7 25.5 × 1.5 = 38.3 < 9500 ÷ 0.362 = 26.24 Km (5682) 83.3 17 65 25 10  23 33.22 (7934) 82.5 2.88 5.6 25.3 × 1.5 = 38 < 9500 ÷ 0.361 = 26.32 Km (5493) 85.3

Embodiment 2

In a certain city, water gas was used as main gas source for civil gas supply. In 1980s, three water gas generators at diameter of 2.26 meter were installed, two of which was for gas generation and the other one was for standby purpose. Daily water gas generation capacity is 60,000 m³ with heat value of 2800 Kcal/nm³. At that moment, the State didn't require heat value of coal gas reaching a high standard but maintaining gas supply for over 20,000 households in the city. However, with deepening of reform and opening up and development of local economy, coal gas users increased to 50,000 after urbanization and city expansion. It is estimated that there're over 80,000 gas users in city proper by 2008.

If municipal planning on fuel gas engineering is refined, it is estimated that over RMB 60 million will be invested on gas generation. It is impossible to use natural gas as city fuel gas.

Preparation method is as follows: filtering liquid light hydrocarbon with 200-mesh strainer, and pressing liquid hydrocarbon mixed with air which is subject to drain spray mixing to pressure of 4 kg/cm²; heating and gasifying the liquid hydrocarbon in the heating gasifier at 120° C., and then mixing 10% gasified liquid hydrocarbon fuel gas below 80° C. with 35% air in a mixing chamber to for mixed light hydrocarbon fuel gas; storing the mixed fuel gas in the middle gas-storing tank after it is tested by oxygen meter; storing the mixed fuel gas after 55% water gas is mixed with light hydrocarbon fuel gas and oxygen content is measured acceptable with oxygen meter; at last, transmitting and distributing the above said mixed fuel gas to user terminal in a low or middle and low pressure two grade form.

Heat value of the mixed fuel gas is improved from former 2800 Kcal/nm³ to current 5330 Kcal/nm³ and output of the mixed fuel gas is increased to 109,000 m³ per day, which makes sure maximum 90,000 households access to gas supply daily. Not only current 50,000 gas users can be satisfied, but also there're still surplus of gas generation and supply by 2008. New increased equipment for gas production plant amounts to less than RMB 8 million. The cost of gas production is reduced from RMB 0.43 to 0.26 per 1000 Kcal/Nm³. Gas supply price is reduced by about 45%, from original RMB 83/month to RMB 48/month. Gas production enterprise will gain profits even if there's no more governmental subsidy.

With more and more natural gas is discovered and explored, liquid natural gas could be used as supplementary gas source for city which is far away from natural gas source when production technology and equipment are improved in the future. Mixed fuel gas which is prepared by mixing 50% water gas, 35% natural gas and 15% air will produce heat value of 4780 Kcal/nm³ with daily production capacity of 120,000 m³. As current technical conditions restrict the development of liquid natural gas, cost of natural gas mixed with air and coal gas is higher than cost of light hydrocarbon mixed with air and coal gas.

As for transmitting and distribution, original main pipe diameter for the city was 500 MM, and the farthest residential quarter is 6.5 KM from the gas production plant according to city planning when gas users increase to 80,000 households.

Pressure drop of unit length is 1.186 mmH₂O/m, and distribution pressure is 0.1 Mpa. Pressure in pressure regulation room for living quarter is greater than or equal to 500 mmH₂O. As (10000 mmH₂O-500 mmH₂O)/1.186 mmH₂O/m=8.01 KM, is greater than 6.5 KM; therefore, original pipeline network could also be used.

Property parameter of 5 R fuel gas which is prepared by mixing the invented fuel gas and civil coal gas is shown in Table 4;

Property parameter of 5 R fuel gas which is prepared by mixing the invented fuel gas and water gas is shown in Table 5;

Property parameter of 5 R fuel gas which is prepared by mixing the invented fuel gas and semi-water gas is shown in Table 6.

TABLE 4 Comparison between UEL × 200,000 household: 1.5 main pipe diameter Wobbe Combus- and 08 m transmitting Civil (Dry) Light Heat value index W tion Combustible pressure 0.1 Mpa unit S/ coal Natural hydrocarbon Air MJ/Nm³ MJ/m³ potency CO gas pressure and max. N gas % gas % % % (Kcal/Nm³) (Kcal/m3) CP O₂ % % concentration % transmitting distance 1 100    15.83    21.15 86 0.4 17.9 42.6 × 1.5 = 63.9 < 9500 ÷ 0.892 = 10.65 Km (3780) (5052) 79.6 2 92 1.6 6.4    17.1    21.78 76 1.71 16.5 39.8 × 1.5 = 59.7 < 9500 ÷ 0.841 = 11.29 Km (4084) (5201) 74.8 3 88 2.4 9.6    17.73    22.07 72.7 2.37 15.8 38.4 × 1.5 = 57.6 < 9500 ÷ 0.818 = 11.61 Km (4235) (5272) 72.5 4 84 3.2 12.8    18.37    22.39 70 3.02 15 37 x 1.5 = 55.5 < 9500 ÷ 0.796 = 11.93 Km (4388) (5347) 70.1 5 80 4 16    19.01    22.69 67.4 3.68 14.3 35.6 × 1.5 = 53.4 < 9500 ÷ 0.775 = 12.26 Km (4540) (5420) 67.7 6 76 4.8 19.2    19.65  23 65.2 4.34 13.6 34.2 × 1.5 = 51.3 < 9500 ÷ 0.775 = 12.58 Km (4692) (5492) 65.3 7 72 5.6 22.4    20.28    23.29 63.3 4.99 12.9 32.8 × 1.5 = 49.2 < 9500 ÷ 0.736 = 12.91 Km (4844) (5562) 62.9 8 68 6.4 25.6    20.91    23.57 61.5 5.65 12.2 31.4 × 1.5 = 47.1 < 9500 ÷ 0.718 = 13.23 Km (4995) (5630) 60.5 9 60 8 32    22.19    24.16 58.4 6.96 10.74 28.7 × 1.5 = 43.1 < 9500 ÷ 0.684 = 13.89 Km (5299) (5771) 55.8 10 60 4.8 6.4 28.8  24    24.12 58.2 6.29 10.74 28.5 × 1.5 = 42.8 < 9500 ÷ 0.686 = 13.85 Km (5157) (5760) 58.9 11 60 12 4 24    20.7    24.08 58.5 5.28 10.74 28.3 × 1.5 = 42.5 < 9500 ÷ 0.688 = 13.81 Km (4944) (5752) 63.6 12 60 19.2 1.6 19.2    19.8    24.09 59.3 4.27 10.74 28.1 × 1.5 = 42.2 < 9500 ÷ 0.687 = 13.83 Km (4730) (5754) 68.4 13 60 24 16    19.21    24.13 60.3 3.6 10.74 27.93 × 1.5 = 9500 ÷ 0.685 = 13.86 Km (4588) (5762) 41.9 < 71.5 14 58 6 6.4 29.6    21.76    24.25 57.4 6.45 10.38 27.8 × 1.5 = 41.7 < 9500 ÷ 0.678 = 14.01 Km (5197) (5791) 58.5 15 100    158.66    103.62 39.2 (37893)  (24749)  16 100    40.47    53.37 40 (9665) (12746)  Note: 1. 5R manual coal gas classified in civil fuel gas means gas with Wobbe index of 21.1-24.3 MJ/m³ and combustion potency of CP 55-96. 2. Pressure of pipeline in pressure regulation room for living quarter is greater than 500 mmH₂O. 3. Heat consumption for each household per day is assumed to be 6500 Kcal/household · day 4. 6R manual coal gas classified in civil fuel gas means gas with Wobbe index of 25.2-29 MJ/m³ and combustion potency of CP 63-110. 5. 7R manual coal gas classified in civil fuel gas means gas with Wobbe index of 30.4-34.9 MJ/m³ and combustion potency of CP 72-128. 6. 1.5 times of Upper Explosion Limit, which is smaller than value of volume content of combustible gas in the mixed fuel gas. Therefore, it is a kind of safe fuel gas.

TABLE 5 200,000 Comparison household: main between UEL × pipe diameter 1.5 0.8 m transmitting Wobbe and pressure 0.1 Mpa (Humid) Light Heat value index W Combustion Combustible unit pressure and Water Natural hydrocarbon Air MJ/Nm³ MJ/m³ potency gas max. transmitting S/N gas % gas % % % (Kcal/Nm³) (Kcal/m3) CP O₂ % CO % concentration % distance 1 55 10 35    22.31    23.75 63.9 7.46 18.9 30.9 × 1.5 = 46.4 < 9500 ÷ (5330) (5672) 58.2 0.707 = 13.44 Km 2 54 7 8 31    21.62    23.68 62.8 6.62 18.6 31.4 × 1.5 = 47.1 < 9500 ÷ (5164) (5656) 62.1 0.711 = 13.36 Km 3 53.5 10.5 7 29    21.28    23.66 62.4 6.2 18.4 30.8 × 1.5 = 46.2 < 9500 ÷ (5082) (5650) 64 0.713 = 13.33 Km 4 53 14 6 27    20.94    23.64 62.1 5.78 18.2 30.3 × 1.5 = 45.5 < 9500 ÷ 0.714 = (5000) (5646) 65.9 13.3 Km 5 52.5 17.5 5 25    20.59    23.61 61.9 5.36 18.1 29.8 × 1.5 = 44.8 < 9500 ÷ (4918) (5639) 67.8 0.715 = 13.28 Km 6 52 21 4 23    20.25    23.61 61.9 4.93 17.9 29.4 × 1.5 = 44.1 < 9500 ÷ (4836) (5638) 69.8 0.716 = 13.27 Km 7 51.5 24.5 3 21    19.9    23.59 61.9 4.51 17.7 30 × 1.5 = 45 < 9500 ÷ (4753) (5635) 71.7 0.717 = 13.26 Km 8 51 28 2 19    19.56    23.6 62 4.09 17.5 28.6 × 1.5 = 42.9 < 9500 ÷ (4671) (5636) 73.6 0.717 = 13.26 Km 9 50 35 15    18.72    23.43 62.7 3.25 17.2 27.9 × 1.5 = 41.9 < 9500 ÷ (4471) (5596) 77.5 0.726 = 13.08 Km 10 100    11.7    15.88 99.2 (2800) (3793)

TABLE 6 200,000 Comparison household: main between UEL × pipe diameter 1.5 0.8 m transmitting Light Wobbe and pressure 0.1 Mpa Semi- (Humid) hydro- Heat value index W Combustion Combustible unit pressure and S/ water Natural carbon Air MJ/Nm³ MJ/m³ potency CO gas max. transmitting N gas % gas % % % (Kcal/Nm³) (Kcal/m3) CP O₂ % % concentration % distance 1 70 10 20    22.55    23.91 55 4.33 18.5 34.8 × 1.5 = 52.5 < 9500 ÷ (5385) (5711) 59.7 0.688 = 13.81 Km 2 68 7 8 17    22.09    24.3 55 3.69 17.4 34.1 × 1.5 = 51.2 < 9500 ÷ (5277) (5800) 63 0.675 = 14.07 Km 3 67 10.5 7 15.5    21.7    24.2 55.1 3.38 17.1 33.4 × 1.5 = 50.1 < 9500 ÷ 0.68 = 13.97 Km (5182) (5784) 64.7 4 66 14 6 14    21.3    24.1 55.2 3.06 16.9 32.7 × 1.5 = 49.1 < 9500 ÷ 0.686 = 13.85 Km (5087) (5760) 66.3 5 65 17.5 5 12.5    20.9  24 55.4 2.74 16.6 31.9 × 1.5 = 47.8 < 9500 ÷ 0.691 = 13.75 Km (4991) (5737) 68 6 64 21 4 11    20.5    23.9 55.6 2.43 16.4 31.2 × 1.5 = 46.8 < 9500 ÷ 0.697 = 13.63 Km (4895) (5715) 69.7 7 63 24.5 3 9.5    20.09    23.8 56 2.11 16.1 30.4 × 1.5 = 45.6 < 9500 ÷ 0.702 = 13.53 Km (4799) (5690) 71.3 8 62 28 2 8    19.69    23.7 56.4 1.79 15.9 29.7 × 1.5 = 44.6 < 9500 ÷ 0.708 = 13.42 Km (4703) (5670) 73 9 60 35 5    18.89    23.57 57.6 1.16 15.3 28.93 × 1.5 = 9500 ÷ 0.718 = 13.23 Km (4511) (5630) 43.4 < 76.3 10 100     9.99    12.72 73.7 (2400) (3037)

Embodiment 3

In a certain county, population is 10,000 households and no pipeline network coal gas is supplied. Main fuel gas for citizens in the county is petroleum gas and coal. However, a fertilizer plant is established 5 kilo miles from the county. Part of emission gas from carbureted water gas in two-stage furnace for purpose of nitrogen fertilizer production is used as boiler fuel and all other part are released to air. Renovation is as follows: 50,000 M³/day down blowing gas from the two-stage furnace is used as fuel of nitrogen fertilizer plant; the other released 1, 5000 M³/day is stored gas-storing tank. All top blowing coal gas is collected for pipeline coal gas. Then we get 11, 3900 M³/day with heat value of 3140 Kcal/Nm³, which could only enough to supply fuel gas for about 5,000 households. However, value of W 17.2 MJ/m³ and CP 86.48 is far beyond that of 5 R fuel gas, i.e., W 21.1-24.3 MJ/m³ and CP 55-96.

Preparation method is as follows: filtering liquid light hydrocarbon with 200-mesh strainer, and pressing liquid hydrocarbon mixed with air which is subject to isopiestic mixing to pressure of 1 kg/cm²; heating and gasifying the liquid hydrocarbon in the heating gasifier at 100° C., and then mixing 8% gasified liquid hydrocarbon fuel gas with 32% air in a mixing chamber to form mixed light hydrocarbon fuel gas; storing the mixed fuel gas in the middle gas-storing tank after it is tested by oxygen meter; storing the mixed fuel gas after 60% two-stage coal gas is mixed with light hydrocarbon fuel gas and oxygen content is measured acceptable with oxygen meter; at last, transmitting and distributing the above said mixed fuel gas to user terminal in a low pressure form. Then we get 189,800 m³ per day with heat value of 4910 Kcal/nm³, which makes sure that 100,000 households in the county are supplied with pipeline gas, and makes other application of remaining 40% gas available to other industries in the county. Combustion characteristics of mixed fuel gas, W22.24 MJ/m³ and CP 60, comply with 5 R civil manual coal gas standard. Fuel appliance could be also produced and sold in standard.

Property parameter of the mixed fuel gas which is prepared by mixing the invented fuel gas with carbureted coal gas and two-stage coal gas is shown in Table 7.

TABLE 7 200,000 Comparison household: main between_UEL × pipe diameter 1.5 0.8 m transmitting Light Wobbe Com- and pressure 0.1 Mpa Carbureted (Humid) hydro- Heat value index W bustion Combustible unit pressure and S/ water Natural carbon Air MJ/Nm³ MJ/m³ potency CO gas max. transmitting N gas % gas % % % (Kcal/Nm³) (Kcal/m3) CP O₂ % % concentration % distance 1 60 8 32    20.56    22.24 60 6.82 11.7 30.2 × 1.5 = 45.3 < 9500 ÷ 0.806 = (4911) (5311) 56 11.78 Km 2 60 6 6.4 27.6    20.22    22.46 59.7 5.89 11.7 29.4 × 1.5 = 44.1 < 9500 ÷ 0.791 = 12.02 Km (4830) (5364) 60.2 3 60 9 5.6 25.4    20.06    22.59 59.7 5.43 11.7 29.1 × 1.5 = 43.7 < 9500 ÷ 0.782 = 12.15 Km (4791) (5396) 72.3 4 60 12 4.8 23.2    19.89    22.73 59.8 4.97 11.7 28.8 × 1.5 = 43.2 < 9500 ÷ 0.772 = 12.31 Km (4751) (5428) 64.4 5 60 15 4 21    19.73    22.87 59.9 4.51 11.7 28.5 × 1.5 = 42.8 < 9500 ÷ 0.763 = 12.45 Km (4711) (5462) 66.5 6 60 18 3.2 18.8    19.56    23.02 60.1 4.04 11.7 28.2 × 1.5 = 42.3 < 9500 ÷ 0.753 = 12.62 Km (4672) (5498) 68.5 7 60 21 2.4 16.6    19.39    23.18 60.7 3.58 1..7 28 × 1.5 = 42 < 9500 ÷ 0.743 = 12.79 Km (4631) (5536) 70.6 8 60 24 1.6 14.4    19.22    23.35 61.3 3.12 11.7 27.8 × 1.5 = 41.7 < 9500 ÷ 0.732 = 12.98 Km (4591) (5576) 72.7 9 60 30 10    18.89    23.74 63 2.2 11.7 28.9 × 1.5 = 43.4 < 9500 ÷ 0.708 = 13.42 Km (4512) (5669) 76.9 10 100    13.11    17.23 86.6 (3131) (4116) 11 100    36.68    46.63 39.44 (8775) (11136)  200,000 Comparison household: main between UEL × pipe diameter 08 m 1.5 transmitting Two- Wobbe and pressure 0.1 Mpa stage (Dry) Light Heat value index W Combustion Combustible unit pressure and S/ furnace Natural hydrocarbon Air MJ/Nm³ MJ/m³ potency CO gas max. transmitting N gas % gas % % % (Kcal/Nm³) (Kcal/m3) CP O₂ % % concentration % distance 55 9 36    21.51    22.8 58.08 7.65 10.73 50 ÷ 30.7 = 1.73 9500 ÷ 0.767 = (5137) (5446) 12.38 Km 55 6 7.2 31.8    21.08    23.0 57.35 6.68 10.73 57.14 ÷ 9500 ÷ 0.758 = 12.53 Km (5035) (5492) 30.92 = 1.85 55 9 6.3 29.7    20.87    23.11 57.26 6.24 10.73 59.21 ÷ 9500 ÷ 0.749 = 12.68 Km (4984) (5519) 30.6 = 1.94 55 12 5.4 27.6    20.65    23.22 57.25 5.8 10.73 61.28 ÷ 9500 ÷ 0.74 = 12.84 Km (4933) (5546) 30.3 = 2.02 55 15 4.5 25.5    20.44    23.35 57.34 5.36 10.73 63.35 ÷ 9500 ÷ 0.731 = 13 Km (4882) (5578) 29.8 = 2.14 55 18 3.6 23.4    20.23    23.5 57.51 4.91 10.73 65.42 ÷ 9500 ÷ 0.72 = 13.19 Km (4831) (5613) 29.72 = 2.2 55 21 2.7 21.3    20.01    23.64 57.81 4.47 10.73 67.49 ÷ 9500 ÷ 0.706 = 13.46 Km (4780) (5647) 29.6 = 2.28 55 24 1.8 19.2    19.80    23.82 58.25 4.03 10.73 69.56 ÷ 9500 ÷ 0.69 = 13.77 Km (4729) (5688) 29.33 = 2.37 55 30 15    19.37    24.19 59.51 3.15 10.73 73.7 ÷ 28.34 = 9500 ÷ 0.681 = (4627) (5777) 2.6 13.94 Km

Embodiment 4

There were 15,000 households who could use pipeline gas from industry off-gas emitted in a fertilizer plant in the old town of a certain city. Several years later, pipeline gas user increased to 60,000 households in following 4 stages, 40,000, 45,000, 50,000 and 60,000 households respectively.

However, the fertilizer plant could provide gas for about 20,000 households to maximum extent, i.e., assuming that daily gas consumption for each household is 6500 Kcal/nm³ on average and industry off-gas is 3100 Kcal/nm³, maximum daily supply amount is 42,000 m³/day. Preparation of light hydrocarbon mixed with air and coal gas will be made into following 4 stages accordingly.

Stage 1: 70% coal gas, 6% light hydrocarbon and 24% air are mixed to generate mixed fuel gas of 60,000 m³/day with heat value of 4472 Kcal/nm³, which could provide gas for 40,000 households on basis of daily gas consumption of 6500 Kcal/nm³ per household;

Stage 2: 65% coal gas, 7% light hydrocarbon and 28% air are mixed to generate mixed fuel gas of 64,600 m³/day with heat value of 4694 Kcal/nm³, which could provide gas for 46,600 households on basis of daily gas consumption of 6500 Kcal/nm³ per household;

Stage 1: 60% coal gas, 8% light hydrocarbon and 32% air are mixed to generate mixed fuel gas of 70,000 m³/day with heat value of 4915 Kcal/nm³, which could provide gas for 52,900 households on basis of daily gas consumption of 6500 Kcal/nm³ per household;

Stage 1: 55% coal gas, 9% light hydrocarbon and 36% air are mixed to generate mixed fuel gas of 76,400 m³/day with heat value of 5137 Kcal/nm³, which could provide gas for 60,400 households on basis of daily gas consumption of 6500 Kcal/nm³ per household.

The four gas generation stages of the embodiment are also provided in table 5 from SN 1 to 4. Wobbe index (W) and combustion potency (CP) of all kinds of mixed fuel gas all meets 5 R fuel gas standard.

The invention intends to generate mixed fuel gas complying with a certain fuel gas standard and complying as well as combustion characteristics of national fuel gas specifications by mixing light hydrocarbon mixed with air with original manual coal gas or industry off-gas or other kinds of coal gas which is not used as pipeline gas till now. When natural gas is used as civil fuel gas, the same preparation method could be used for generation of mixed fuel gas, combustion characteristics of which will remain unchanged. The preparation method allows for mixing and replacing between different gas sources and enables the city access to multiple gas sources. As a result, fuel gas supply of the city won't be affected when a certain gas supply is cut off due to unexpected reasons. 

1. A production method for civil mixed fuel gas with light hydrocarbons mixed with air and coal gas, which is characterized in that the preparation method of the said civil mixed fuel gas is as follows: a. filtering liquid light hydrocarbons, and pressuring; b. heating and gasifying the light hydrocarbons in the heating gasifier; c. mixing gasified hydrocarbons with air or pressured air in a mixing chamber to form a mixture of light hydrocarbons and air; d. storing the mixture in a middle gas-storing tank after measured by oxygen meter; e. mixing coal gas and light hydrocarbons mixed with air in a gas-mixing chamber to form mixed fuel gas; f. storing the mixed fuel gas in a gas-storing tank after measured by oxygen meter; g. transmitting and distributing the mixed fuel gas to user terminal in a low or middle and low pressure two grade form.
 2. A production method of civil mixed fuel gas with light hydrocarbons mixed with air and coal gas according to claim 1, wherein the preparation method of the said civil mixed fuel gas is as follows: a. filtering liquid light hydrocarbons with a 200-mesh strainer and pressuring liquid light hydrocarbons mixed air which is subject to drain spray mixing to ≧3 kg/cm² and liquid light hydrocarbons mixed air which is subject to isopiestic mixing to ≧0.8 kg/cm²respectively; b. heating and gasifying light hydrocarbons in the heating gasifier to a temperature ≧110° C. for light hydrocarbons subject to drain spray mixing and to a temperature ≧80° C. for light hydrocarbons subject to isopiestic mixing respectively; c. mixing gasified hydrocarbons with air or pressured air in a mixing chamber to form a mixture of light hydrocarbons and air; d. storing the mixture in a middle gas-storing tank after measured by oxygen meter; e. storing the mixture of natural gas, coal gas and light hydrocarbons mixed with air after oxygen content is measured acceptable by oxygen meter; f. transmitting and distributing the said mixed fuel gas to user terminal in a low or middle and low pressure two grade form.
 3. A production method of civil mixed fuel gas with light hydrocarbons mixed with air and coal gas according to claim 1, wherein oxygen content is measured to be within 0.5-10% by oxygen meter.
 4. A production method of civil mixed fuel gas with light hydrocarbons mixed with air and coal gas according to claim 1, wherein liquid light hydrocarbons is a compound of over following one or two substances: by-product liquid light hydrocarbon in petrochemical engineering, decomposed light hydrocarbon in petrochemical engineering or condensate light hydrocarbon in petrol and natural gas.
 5. A production method of civil mixed fuel gas with light hydrocarbons mixed with air and coal gas according to claim 1, wherein the mixed fuel gas is prepared and mixed of 1.6-10% light hydrocarbon fuel gas, 4-36% air and 55-94.4% coal gas.
 6. A production method of civil mixed fuel gas with light hydrocarbons mixed with air and coal gas according to claim 1, wherein low pressure refers to pressure ≦500 mmH₂O and middle pressure refers to pressure of 500 mmH₂O-0.1 Mpa.
 7. A production method of civil mixed fuel gas with light hydrocarbons mixed with air and coal gas according to claim 2, wherein the mixed fuel gas is prepared and mixed of 4.8-34% natural gas, 8-31.8% air, 1.6-8% light hydrocarbon fuel gas and 50-70.6% coal gas. 